A gas discharge (e.g. fluorescent) lamp typically utilizes a ballast circuit to convert an a.c. line voltage to a high frequency bidirectional voltage, which is then impressed across a resonant load circuit containing the gas discharge lamp. The resonant load circuit includes a resonant inductor and a resonant capacitor for setting the frequency of resonance of current in such circuit. The ballast circuit includes a converter, of the series half-bridge type, for instance, that includes a pair of switches for alternately connecting one end of the resonant load circuit to a d.c. bus voltage and then to ground; in this way, the mentioned bidirectional voltage is impressed across the resonant load circuit.
A ballast circuit of the foregoing type is disclosed in co-pending U.S. patent application Ser. No. 08/020,275, filed Feb. 18, 1993, allowed Sep. 24, 1993, entitled "Electronic Ballast Arrangement for a Compact Fluorescent Lamp," by Louis R. Nerone, the present inventor; such application is assigned to the present assignee, and its disclosure is incorporated herein by reference. The disclosed power supply circuit utilizes feedback circuitry for controlling the mentioned pair of switches of the converter. A signal representing a current in the resonant load circuit is fed back to a pair of gate-control circuits for controlling the switching state of the mentioned pair of converter switches; each gate-control circuit has a transformer winding coupled to receive the foregoing feedback signal. During steady state operation, the gate-control circuits operate in a regenerative, or self-resonant, manner. To initiate the alternate switching of the converter's switches, an additional winding is coupled to a transformer winding of one of the gate-control circuits. A pulse of current is generated on the additional winding so as to be impressed across the gates of the converter switches, to initiate start-up of a regenerative mode of operation of the converter switches.
While being effective for starting the ballast circuitry, it would be desirable to avoid the cost of the additional winding, and, where ballast size is limited, to avoid the added bulk required to incorporate the additional winding.